Is api.posm service attempting to connect to host port 80?
From the compose-file web page, describing ‘ports:’
" Either specify both ports ( HOST:CONTAINER ), or just the container port (an ephemeral host port is chosen)."
So, catalogmanager.services.posm is on some ephemeral host port, not 80.
If api.posm is attempting to connect to the host interface port 80, then the above matters.
Secondly, I’m confused by the dots in the service name. I’ve never used them. I’ve also not attempted to use fqdn type names as service names. No need. I wonder if the dns client inside docker is confused too. I don’t know if this is root cause. Are you opposed to using simple service names (without the dots)? I don’t think it will resolve the connection problem. I do not know if its a problem.